The present invention relates to a new and improved apparatus and method for use in supplying ink during operation of a printing press.
During operation of offset lithographic printing presses, inker assemblies have been used to provide a flow of ink to plate rolls and blanket rolls of the printing press. A known inker assembly includes a pump assembly having a piston which is reciprocated through intake and discharge strokes by a drive assembly to pump ink to a rail or manifold.
The known inking mechanism includes a piston which is moved axially through intake and discharge strokes. The intake and discharge strokes are of equal duration. This results in a pulsating supply of ink from the pump assembly. Thus, during the discharge stroke of the piston, ink flows from the pump assembly. During the intake stroke of the piston, ink does not flow from the pump assembly. Since the intake and discharge strokes are of equal duration, the pump assembly is effective to discharge ink only during one-half of the press operating time.
During operation of the printing press disclosed in the prior art, the speed of operation of the pump assembly varies as a direct function of variations in printing press operating speed. Therefore, when the printing press is operated at a relatively slow speed, the time required for an intake stroke of the piston becomes relatively long. This results in an interruption in the discharge of ink from the pump assembly for a relatively long period of time.
The ink pump assembly of the aforementioned prior art has a piston which is reciprocated and rotated by rotation of a crank member. The speed at which the crank member moves the piston during a discharge stroke of the piston will vary. Thus, the speed of movement of the piston is the fastest during a central portion of the discharge stroke and is slowest at opposite end portions the discharge stroke. This results in an uneven flow of ink from the pump assembly during the discharge stroke of the piston.
Due to the extremely uneven flow of ink from the pump assembly shown in the aforementioned prior art, the quality of the printed product cannot be maximized. Thus, ink flows from the pump assembly only during the discharge portion of the operating cycle and does not flow from the pump assembly during the intake portion of the discharge cycle. Since the intake and discharge portions of the pump operating cycle are of equal duration, during half of the time the pump assembly is operating, the pump assembly is ineffective to discharge ink. In addition, during the discharge portion of the pump operating cycle, the flow rate of ink from the pump assembly varies from a very low flow rate at the ends of the discharge portion of the pump operating cycle to a relatively large flow rate at the center portion of the pump operating cycle.
Since the rate of flow of ink from this known pump assembly is very uneven, there is an over supply of ink during a portion of the pump operating cycle and an insufficient supply of ink during another portion of the pump operating cycle. Of course, the uneven supply of ink is detrimental to the quality of the printed product. Other known ink supply mechanisms for use in association with printing presses are disclosed in U.S. Pat. Nos. 4,461,209; 4,281,597; and 3,018,727.